Synthetic food colorants are steadily being replaced by natural ones because of consumer preferences. Anthocyanins (polyphenolic pigments) are natural, water-soluble nontoxic pigments derived from fruits and vegetables, displaying a variety of colors from orange to blue. Because of their antioxidant properties, they may also have beneficial influence on human health (Shenoy, V. R., 1993, Curr. Sci. 64: 575-579). A drawback in the use of anthocyanins as food colorants is their low stability. In fact the color stability of anthocyanins depends on a combination of factors including chemical nature of anthocyanins, their concentration, pH, temperature and presence of complexing agents such as metal ions and phenolic compounds (Markakis, P., 1982, In: Markakis, P. (Ed.) Anthocyanins as Food Colors, Academic Press, New York, pp 163-180).
Common sources of anthocyanins used commercially as natural food colorants are grape skin extract, red cabbage, purple carrot, and elderberry. They are natural pH indicators, being red in acidic conditions where they are most stable and becoming bluer and more unstable as the pH increases. Thus, a source of stable natural blue color that can be used in the food and beverage industry remains to be identified.
Anthocyanins are produced by chopping or crushing the fruit or vegetable and subsequent infusion of water acidified with a common food acid. This extract is then concentrated by non-chemical separation techniques. Pigment extracts from plant sources generally contain mixtures of different anthocyanin molecules, which vary by their level of hydroxylation, methylation and acylation. These factors can vary in the source plant from year to year, and are influenced by weather and environmental factors. Thus, another challenge for the commercial production of anthocyanin pigments from plants is that harvest is often limited to once a year. This means a large volume of extract has to be prepared and stored for an extended period of time to supply the needs of the food industry throughout the year. Special storage conditions often have to be available due to the instability of anthocyanins.